The present invention relates to stable pharmaceutical and veterinary preparations for topical and nasal uses containing amorphous calcium mupirocin, also known as amorphous calcium pseudomonate as active ingredient therein.
Mupirocin is an antibiotic produced by aerobically culturing Pseudomonas Fluorescens. From the isolated Mupirocin, the calcium salt can be prepared.
Mupirocin and derivatives are mainly active against gram positive aerobes and some gram negative aerobes (Martindale p. 227, 32 ed., 1999). Mupirocin free acid, its salts and esters are described in UK patent # 1,395,907. These agents are found to be useful in treating skin, ear and eye disorders.
Currently, in the US market, there are three commercial products, which contain Mupirocin free acid or crystalline Mupirocin calcium dihydrate, as the active ingredients. These products are Bactroban(copyright) Ointment, Bactroban(copyright) Nasal and Bactroban(copyright) Cream, manufactured by SmithKline Beecham. The first contains Mupirocin, while the other two contain crystalline Mupirocin Calcium dihydrate.
The formulation of Bactroban(copyright) Ointment is protected under U.S Pat. No. 4,524,075. The formulation of Bactroban(copyright) Nasal is described in U.S Pat. No. 4,790,989. The cream base of Bactroban(copyright) Cream is described in world patent # 95/10999 and U.S Pat. No. 6,025,389.
Crystalline mupirocin calcium, its properties and methods of preparation are described in detail in U.S Pat. No. 4,916,155. This patent emphasizes on the improved thermal stability of the crystalline dihydrate form of the calcium salt. While at the same time, its poor solubility in water is mentioned as well. However, the poor solubility in water and in other hydrophilic solvents limits the formulation possibilities of this compound.
Furthermore, poor solubility of a drug substance in water may reduce its bioavailability within the body (Hancock and Zografi, J. Pharm. Sci., vol. 86, January 1997).
The dissolved state of the active ingredient within the formulation is preferred over the suspended form. In order to achieve a good clinical effect, the active ingredient has to reach the target area as soon as possible. This process involves two steps: dissolution and diffusion. By allowing the active substance to be dissolved within the formulation, we skip the first step of dissolution and obviate the second and hence, shorten the time it takes the active to reach the target area. In other words, keeping the active substance in a soluble state might increase the bioavailability. Thus a compound that will be both thermally stable and soluble in hydrophilic solvents will broaden the formulation scope of mupirocin.
Surprisingly, we found that unlike crystalline mupirocin calcium dihydrate, the amorphous compound is soluble in hydrophilic solvents. However, the different solubility profile, is not enough for formulation development because, as mentioned before, the amorphous material is claimed to be less thermally stable than the crystalline form.
We also found that we can overcome this stability problem by using a solution of the amorphous form in hexylene glycol. This solution was surprisingly found to be stable.
These findings enable us to formulate the amorphous forms of mupirocin calcium, for topical, nasal and other uses, in formulations such as creams, ointments, gels, solutions, sprays and other preparations not mentioned here.
Thus, according to the present invention, there is now provided stable pharmaceutical preparations for topical and nasal uses, comprising Mupirocin calcium amorphous as an anti-microbial active agent therein, dissolved in a pharmaceutically acceptable solvent providing stability therefore.
In preferred embodiments of the present invention, said Mupirocin calcium amorphous is dissolved in hexylene glycol.
In especially preferred embodiments of the present invention, said preparation comprises a hydrophilic phase consisting of Mupirocin calcium amorphous dissolved in Hexylene glycol, in admixture with one or more hydrophilic additives, dispersed in a hydrophobic phase, to create an essentially waterless cream.
In said embodiments, said hydrophilic additives are preferably selected from the group consisting of PEG 400, Propylene Carbonate, Butylene Glycol; and other pharmaceutically accepted additives.
In especially preferred embodiments, there is provided a cream preparation wherein the hydrophobic phase comprises an oleaginous base selected from the group consisting of petrolatum and hard fat; stiffening agents that are selected from the group consisting of cetostearyl alcohol, cetyl alcohol and stearyl alcohol; humectants selected from a group consisting of castor oil and oleyl alcohol; surfactants selected from the group consisting of a surfactant with an HLB equal to or below 5, and other pharmaceutically accepted additives.
The following table presents the solubility of mupirocin calcium amorphous, compared to the solubility of the crystalline form, in various pharmaceutically acceptable hydrophilic solvents. We prepared 2% solutions (calculated as free acid), similar to the commercially available products.
The results show clearly the different behavior of the amorphous compound, compared with the crystalline one. The amorphous form is much more soluble in hydrophilic solvents. As mentioned above, this property provides us the opportunity to develop a wide range of pharmaceutical preparations for topical and nasal use, where the mupirocin calcium is in a dissolved state.
Mupirocin calcium amorphous is claimed to be less stable than the crystalline form. In order to be able to use the 2% solutions of Mupirocin calcium amorphous presented in the previous table, we have to ensure that the solutions are chemically stable.
The stability of Mupirocin Calcium amorphous in various acceptable pharmaceutical solvents was tested by heating a 2% solution to 80xc2x0 C. for 24 hours or by heating it to 40xc2x0 for 1 month. Bactroban cream was used as a reference. The results are presented in the following table:
It has to be noted that at 80xc2x0 C. Bactroban Cream undergoes a phase separation. This explains the high percentage of impurities at 80xc2x0 C. after 24 h.
The results presented in table 2, demonstrate the good stability of Mupirocin Calcium amorphous in Hexylene Glycol in absolute and relative terms. The stability of Mupirocin Calcium amorphous in Hexylene Glycol is not mentioned in the prior art. It is further to be noted from the data presented in Table 2 that Hexylene Glycol is a surprisingly preferred solvent, since mupirocin calcium amorphous decomposes to a significant amount in other similar pharmaceutically acceptable polyols.
The discovery of the stable solution of Mupirocin calcium amorphous in Hexylene Glycol provides us several possibilities for pharmaceutical preparations, such as ointments, creams, lotions, solutions and other topical preparations which are not mentioned herein. The invention is demonstrated but not limited to, in the following examples. Usually the mupirocin calcium amorphous is first dissolved in hexylene glycol and then mixed with the other ingredients.